Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Bugfix: cacert should suppot insecure mode if needed

    currently, we use env variable "OS_CACERT" to specify the location of
    cert file. but if there's no cacert and use for personal verification,
    it's better to also support insecure mode by set OS_CACERT=False

    JIRA: YARDSTICK-616

    Change-Id: I73b0860863bf6386f9114328c52594ef87e02fa3
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>
    (cherry picked from commit aa477334a3cb2e49c4343f66bff44c89d7edcf24)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 2f9126f..ac370f9 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 2f9126f350bff38eec2ff452866e5a2ca3d0bdd7
+Subproject commit ac370f93eb345f9aee456cb19724902587c10209